The disclosure of Japanese Patent Application No. 2001-297678 filed on Sep. 27, 2001, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a fuel vapor adsorption apparatus disposed in an intake air passage of an internal combustion engine in order to adsorb fuel vapor and a method of desorbing fuel vapor from a fuel vapor adsorbent.
2. Description of Related Art
As regulations on fuel vapor (hereinafter referred to as xe2x80x9cHCsxe2x80x9d) discharged from a motor vehicle while the vehicle is stopped become more and more stringent, it has become a major issue that HCs diffuse and leak through an inlet port into the atmosphere while the vehicle is stopped. HCs are generated when residual fuel left in an engine and fuel that leaks from an injector vaporize. There has been devised a device, in which an HC adsorbent in the form of, for example, a filter accommodating an active carbon is disposed in a partial or entire surface of a cross section of an intake passage, such as an intake duct, an air cleaner, or the like, to adsorb HCs and thereby prevent HCs from leaking out through the intake port.
According to the device, the adsorbent is purged by air which is drawn in while the vehicle is operating such that HCs previously adsorbed while the vehicle was stopped are desorbed, thereby recovering the adsorption performance of the adsorbent. Thus, the adsorbent can effectively adsorb HCs when the vehicle is stopped the next time. However, the intake air may not be in uniform contact with the adsorbent and if the amount of the intake air is small depending on an operating state of the engine, HCs adsorbed by the adsorbent may not be completely purged. In this case, the adsorbent lacks a sufficient adsorption capacity when the vehicle is stopped the next time. As a result, HCs may leak through the intake port.
There is a known device as disclosed in Japanese Utility Model Laid-Open Publication No. 62-184162, in which an adsorbent provided in an air cleaner is heated to recover the adsorbent. However, since the arrangement has been devised for preventing icing, what is adsorbed by the adsorbent is water content in the air. The control of heating the adsorbent presented in this arrangement is not suited for the desorption of HCs as an object of the invention. Moreover, heating the adsorbent at all times aggravates fuel economy and should be avoided as much as possible.
The inventors have been paying attention to the fact that desorption of HCs adsorbed by an active carbon is promoted under a low pressure or a high temperature condition. At the time of desorption of HCs from the active carbon, HCs adsorbed through liquefaction are desorbed through vaporization. Desorption performance is therefore enhanced under a condition that allows HCs to vaporize easily (high temperature, low pressure). According to the invention, therefore, the desorption performance is enhanced by, reducing the pressure of the place in which the HC adsorbent is disposed, and/or heating the intake air or the HC adsorbent (it is desirable that the air or material be heated to a level of a typical boiling point of a fuel or higher) while the vehicle is operating (or during desorption). This approach makes it possible to efficiently desorb HCs from the adsorbent even with a small amount of air.
A first aspect of the invention relates to a fuel vapor adsorption apparatus of an internal combustion engine. The apparatus includes an adsorbent, disposed on at least a part of a cross section of an intake air passage of the internal combustion engine, that adsorbs fuel vapor, and an adjustment device, disposed upstream of the adsorbent in the intake air passage, that adjusts the amount of the intake air. The apparatus includes a controller that controls the adjustment device to place the adsorbent in a more vacuum condition than condition during an ordinary control of the internal combustion engine, under the same operating state but where fuel vapor is not being desorbed from the adsorbent, by regulating the amount of the intake air while a control is provided to desorb fuel vapor from the adsorbent.
As a result, by controlling the controller of the adjustment device (for example, an intake throttle valve), the adsorbent when purged, is placed in the more vacuum condition than a condition during the ordinary control where fuel vapor is not desorbed from the adsorbent, as compared to the internal combustion engine the same operation state, under but when description is not taking place. This promotes desorption of HCs.
A second aspect of the invention relates to a fuel vapor adsorption apparatus of an internal combustion engine. The apparatus includes an adsorbent, disposed in at least a part of a cross section of an intake air passage of the internal combustion engine, and a heading device. The adsorbent adsorbs fuel vapor. The heating device heats the adsorbent. The apparatus includes a controller that controls the heating device to adjust a heating amount for heating the adsorbent during a desorbing control of the internal combustion engine for desorbing fuel vapor from the adsorbent. The fuel vapor is described in accordance with the amount of the intake air passing through the intake air passage of the internal combustion engine.
In the second aspect, because the heating amount is controlled in accordance with the amount of the intake air passing through the intake air passage, it is possible to efficiently desorb HCs from the adsorbent.
A third aspect of the invention relates to a method of desorbing fuel vapor from an absorbent that adsorbs the fuel vapor and is disposed on at least part of a cross section of an intake air passage of an internal combustion engine. The method includes the step of determining whether a condition for desorbing fuel vapor from the adsorbent is met, and placing the adsorbent, if it is determined that the condition for desorbing fuel vapor from the adsorbent is met, in a more vacuum condition than during an ordinary control of the internal combustion engine under the same operating condition but where fuel vapor is not desorbed from the adsorbent.
In the third aspect, it is possible to efficiently desorb HCs from the adsorbent because the adsorbent is placed in the more vacuum condition if it is determined that the condition for desorbing fuel vapor from the adsorbent is met, than during the ordinary control of the internal combustion engine under the same operating state.
A fourth aspect of the invention relates to a method of desorbing fuel vapor from an adsorbent that adsorbs the fuel vapor and that is disposed on at least part of a cross section of an intake air passage of an internal combustion engine. The method includes the steps of determining whether a condition for desorbing fuel vapor from the adsorbent is met, determining an amount of the intake air required by the internal combustion engine, and increasing a heating amount for heating the adsorbent based on the determined amount of the intake air, if it is determined that the condition for desorbing fuel vapor from the adsorbent is met. The heating amount increases as the determined amount of the intake air decreases.
In the fourth aspect, because the heating amount is controlled in accordance of the intake air passing through the intake air passage, it possible to efficiently desorb HCs from the adsorbent.